All known natural calcitonin peptides contain an amino acid sequence of 32 amino acids. Salmon calcitonin, for example, has the following formula: ##STR1##
In U.S. Pat. Nos. 3,926,938, 4,062,815, 3,929,758, 4,033,940 and 4,217,268 are disclosed improved syntheses of calcitonins including the salmon calcitonin above referred to.
The natural calcitonins include the salmon, eel, bovine, porcine, ovine and human calcitonins. All of these have arginine or threonine at position number 21.